Muffler

ABSTRACT

A tubular housing is subdivided by an annular resonance wall into two compartments. One of the compartments is further subdivided into two chambers by a partition wall. A first pipe extends through one end of the housing and through one of the chambers to communicate with the other chamber which is proximal to the other of the compartments. A second pipe extends through the other end of the housing and through the other compartment and the resonance wall to communicate also with the other chamber.

United States Patent 1151 3,642,095 Fu'ii [45] Feb. 15, 1972 154] MUFFLER 2,071,351 2/1937 McNamara ..181/57 2,205,899 6/1940 Chipley 181/57 [721 Invent JaPa" 2,580,564 1/1952 Ludlow ...l81/48 [73] Assignee: Kabushiki Kajsha F jii Koyg T k 3,166,151 1/1965 Powers ..l81/54 Ja an p Primary ExaminerStephen J. Tomsky [221 Flled= 6, 1969 AttorneyMichae1S. Striker 21 A 1. N 804 934 l 1 pp 0 1571 ABSTRACT 30 F A f Pri D a A tubular housing is subdivided by an annular resonance wall I 1 orelgn pp on y a into two compartments. One of the compartments is further Mar. 22, 1968 Japan ..43/21862 subdivided into two chambers by a partition wall. A first pipe extends through one end of the housing and through one of [52] US. Cl ..l8l/57, 181/59, 181/47 the chambers to communicate with the other chamber which [51] Int. Cl .F0ln 1/04, F011! 1/ 10, FOln 1/16 is proximal to the other of the compartments. A second pipe [58] Field of Search ..181/47, 48, 50, S4, 56, 57, extends through the other end of the housing and through the 181/59 other compartment and the resonance wall to communicate also with the other chamber.- [56] References Cited 7 Claims, 11 Drawing Figures UNITED STATES PATENTS 1,735,789 11/1929 Powell ..l81/59 Q Q o g 8 T /X)( a PATENIEDFEB 15 1912 3.642.095

sum 2 {1F 3 INVENT OR SIIOZ 0 Fu r1;-

ATTORNEY MUFFLER BACKGROUND OF THE INVENTION This invention relates to a device for reducing sound. Known devices of this type, also known as mufflers, are not SUMMARY OF THE INVENTION An object of this invention is to provide a muffler which reduces all kinds of sound, especially low-pitched sound originating due to fuel combustion.

Another object of this invention is to provide a muffler which reduces the higher pitch sounds of machines like blowers or compressors due to a resonance function of the muffler.

A further object of this invention is to provide a muffler for low-pitched sound which requires no sound absorbents or other combustible materials and is capable of withstanding substantial heating, provides improved safety and durability of operation, as well as a more effective muffling of the sound.

A concomitant object of this invention is to provide a muffler which is adjustable to the resonance of frequency of sound to be muffled by making it possible to change the volume of its resonance chamber and the dimensions of resonance holes provided in the muffler.

Still further object of this invention is to provide a muffler which muffles low-pitched sound stepwise.

Yet an additional object of this invention is to provide a muffler for reducing sounds effectively by branching and deflecting the sound carrier stream.

Briefly stated, one feature of the invention involves the provision of a tubular housing which is subdivided by an annular resonance wall into two compartments. One of these compartments is further subdivided by a partition wall into two chambers one of which is farther from and the other of which is closer to the other compartment. A first pipe extends through one end of the housing and through the one chamber, and communicates with the other chamber. A second pipe extends through the other end of the housing and through the other compartment and the resonance wall; it, also, communicates with the other chamber.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a longitudinal sectional view of an embodiment of a muffler for all sound ranges having a variable adjustment device for adjusting it to the requisite resonance frequency;

FIG. 2 is a sectional view taken on line II-II of FIG. 1;

FIG. 3 is a longitudinal sectional view of another type of muffler for all sound ranges;

FIG. 4 is a sectional view on line IV-IV of FIG. 3;

FIG. 5 is a sectional view on line V-V of FIG. I, which shows a device for muffling sound of high and medium pitch;

FIG. 6 is a longitudinal sectional view of an embodiment of a muffler for muffling the low-pitched sound of a boiler;

FIG. 7 is a longitudinal sectional view of an embodiment of a multistage muffler;

FIG. 8 is a longitudinal sectional view of an embodiment of a muffler similar to that of FIG. 7 but with an added device for muffling sound of high and medium pitch;

FIG. 9 is a longitudinal sectional view of another embodiment of a muffler which has a device for branching and deflecting the airstream;

FIG. 10 is a longitudinal sectional view of another embodiment which has a device for muffling sound of high and medium pitch; and

FIG. 11 is a longitudinal sectional view of another embodiment of a muffler for muffling low-pitched sound.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the various Figures, like reference numerals indicate like elements.

In the embodiment of FIG. 1, reference numeral 1 indicates a body or housing of a muffler which has inlet and outlet openings 2,3. Reference numeral 4 indicates a partition or resonance wall of a device for low-pitched sound resonance; it is of annular configuration and provided with a central opening 5 and with resonance holes 6 which are scattered about the opening Wall 4 divides housing 1 into two compartments a, b of which the latter is a resonance compartment 7 with which the holes 6 communicate. Reference numeral 8 indicates an air pipe which passes through resonance compartment 7 and extends through the center opening 5 of wall 4. The other compartment a is subdivided with a partition wall 4a to create two chambers 9, l0. Numeral 10 indicates one of these chambers which is closer to the inlet opening 2 than the chamber 9 and which constitutes part of a device for mufiling sound of high and of middle pitch. Through this closed chamber 10 extends an air supplying pipe 11 which has many sound absorption holes 12; and in the chamber 10, surrounding the pipe 11. there is accommodated sound absorbent means, such as glass wool. The other of these chambers is identified with reference numeral 9 and constitutes a sound scattering chamber with which the pipe 8 communicates.

In the embodiment of FIGS. 2 and 2 the wall 4 has a ringshaped outer wall portion 14 which is exteriorly threaded at 15; the threads 15 mate with corresponding threads 16 provided in the inner surface of the wall of housing 1 so that the wall 4 can be axially displaced relative to the housing 1. The inner side of wall portion 14 is provided with an annular set of teeth 17 (partly shown in FIG. 2); these teeth engage with corresponding teeth provided on a gear wheel 19 which is mounted on a rod-shaped extension 18a of a handle 18. The portion 18a is mounted at 18b for rotation and the handle 18 is accessible exteriorly of housing 1. Turning of handle 18 causes turning of gear 19 and concomitant angular displacement of wall 14 about its axis so that the wall 4 moves axially of housing 1; depending upon its direction of movement, this will result in an increase or a decrease of the volume of compartment 7, so that the resonance action thereof may be matched to the requirements dictated by the sound to be muffled.

Another way of changing the volume of the resonance compartment 7 would be to mount therein a movable divider 20 (shown in chain line in FIG. 1), which is annular like the wall 4 and threaded in the same way. Its displacement would be effected by a handle 21 configurated and operating in the same manner as the handle 18.

It is also possible-although not illustrated-to vary the volume of the resonance compartment 7 by providing the wall 4 (or the movable divider 20) with screw threads in the surfaces bounding their respective central apertures, and forming the outer surface of the pipe 8 with mating threads.

In the embodiment of FIGS. 3 and 4 the cross-sectional areas of the resonance holes 6 of wall 4 are to be varied. A backup wall 22 is back-to-back with the turnable wall 4 and provided with holes 23 corresponding to the holes 6. Handle 25 here replaces the handle 18 of FIGS. 1 and 2, and gear 26 replaces gear 19. By rotating the wall 4 the holes 6 and 23 can be in register fully or partially; the latter possibility is shown in FIG. 4 where it will be seen that the cross-sectional area of holes 6 can be varied depending upon the extent to which holes 6 are out of precise registry with the corresponding holes 23.

Rotation of the wall 4 can, of course, also be effected by another means.

For varying the cross-sectional area of the resonance holes 6 it is good, also, to provide the holes 6 with conical extensions which can project towards the holes 23 of backup wall 22.

In the embodiments of FIGS. l-2 and 3-4, the resonancetype sound reducing device for low-pitched sound is combined with a device for sound of high and medium pitch, accommodated in the chamber 10. The pipe 11 thereof is coaxial with the pipe 8 to assure smooth flow of the sound-carrying fluid stream, and to reduce the resistance to such fluid flows. FIG. 5 is a section on line V-V of FIG. 1, showing the device for suppressing sounds of high and medium pitch; a section taken on a similar section line in FIG. 3 would be identical. The mufflers shown in FIGS. 1-4 operate to muffle sounds of all pitch ranges.

FIG. 6 shows a simple embodiment of a muffler for a boiler chimney using a resonance device a to muffle low-pitched sound originating in operation of the boiler. The same reference numerals as in FIG. 1 designate the same elements. Here, however, the wall 4 is placed with a wall 4' which is of concave-convex shape and rigid with the pipe 8. The sound enters at the inlet 2which is made to communicate with the chimney or the likeand passes through a scattering chamber 9 to the wall 4'.

This embodiment is for muffling of fixed low pitched sound, because the volume of the resonance compartment 7 and the cross-sectional areas of the resonance holes 6 are themselves fixed and cannot be varied to accommodate the muffler to pitch changes.

FIGS. 7 and 8 are essentially embodiments in which two of the mufflers of FIG. 6 have been combined longitudinally, so that two of the resonance devices a are located between the openings 2 and 3. FIG. 7 shows a muffler for low-pitched sound, and the embodiment of FIG. 8 shows a muffler for suppressing sound of all pitch ranges.

An air pipe 8 is mounted in the central portion of the housing 1, and fixed resonance walls 4" and 27 are rigid with its opposite axial ends. The walls 4" and 27 form with the housing I and the pipe 8a an annular resonance compartment with which resonance holes 6 provided in the wall 4' communicate. In addition, resonance wall 4 is rigid with the pipe 8. There are thus provided two devices a which are connected in series, so that the muffler is able to reduce sound twice (or more, if additional devices a are provided). It is desirable for the pipe 8a to be'coaxial with the openings 2 and 3 to diminish resistance to the flowing of fluid through the muffler.

As shown, the walls 4, 4 and 27 may be of one piece with the housing I.

FIG. 8 differs from FIG. 7 in the addition of an air pipe (or pipe portion) II which is positioned between the two devices a and has many sound absorption holes 12 which communicate with absorbent means 13 such as glass wool accommodated in the closed chamber formed by the pipe 11 and the housing 1. Thus, the embodiment of FIG. 8 muffles not only low-pitched sound but, because of these structural differences, also sounds of high or medium pitch.

In the embodiments above mentioned, openings 2,3 of the housing 1 are coaxial with the pipes 8, 8a and/or 11 to reduce the flow resistance encountered by fluid passing through the muffler, and to also reduce noise smoothly and efficiently. In FIGS. 9-11, however, the fluid stream is branched and deflected to increase its flow path and prevent incomplete muffling due to too short a flow path.

In the embodiments of FIGS. 9 and a muffler body 1 has openings 2,3 as before; it also has a plurality of branch pipes 28 whose axes are parallel to but laterally offset from the axis of the housing 1. In FIG. 9 two (or more) branch pipes 28 are supported by a partition wall 29; in FIG. 10 similar branch pipes 28 are supported between concave-convex partition walls 29 and 30. Intermediate the wall 29 and the resonance wall 4' in FIG. 9, and intermediate the walls 30 and 4 in FIG. 10, a sound scattering chamber 9 is formed. At the other side of the respective wall 4' is located the muffler device a for muffling a low-pitched sound which has been previously described. The sound-carrying fluid enters at opening 2, impinges on the wall 29 and is deflected to pass through the branch pipes 28. After traversing the chamber 9, it impinges at the surface P of wall 4 to thereupon pass into and through the pipe 8. This repeated deflection and scattering is effective in reducing the sound resonance.

In FIG. 10, which is basically similar to FIG. 9, the branch pipes are additionally provided with a plurality of sound-absorbing holes 12 which communicate with a chamber defined by the walls 29 and 30, the housing 1 and the branch pipes 28,

and which is filled with sound absorbent means 13, such as glass wool. For this reason, the embodiment of FIG. l0 has an additional device b which is effective for muffling sound of high and medium pitch.

FIG. 11, finally, embodies a muffler for low pitched sound and is a variation type of the FIG. 6 embodiment.

The sound scattering chamber 9 is here located immediately inwards of the inlet opening 2. Its inner end is closed by the wall 4' whose central portion has a surface on which incoming sound and fluid impinge at P. Two or more branch pipes 28 extend from the wall 4 toward the outlet opening 3, being offset from the axes of openings 2 and 3. Their opposite ends penetrate an additional partition wall 30 which defines with the wall 4', the pipes 28 and the housing 1 the resonance compartment 7. The holes 6 in wall 4 communicate with the compartment 7. This construction is efiicient in muffling lowpitched sound by resonance and by branching and deflecting of the waves.

FIG. 1 1 shows only one device a for low-pitched sound, but it is possible to provide two or a multiplicity of such devices, analogously to the modification of FIG. 6 which is shown in FIG. 7, and to thereby further improve the muffling efficiency.

The principle of operation of this invention is as follows:

Generally speaking, when the resonance phenomenon is used for muffling low-pitched sound, the resonance frequency f is given as l I J3 Vl wherein C: Velocity of sound S: Dimension of resonance hole 6 1: Thickness of wall 4 which has the resonance hole 6 V: Volume of the resonance compartment 7.

This formula indicates that it is possible to vary the resonance frequency f to the desired value by changing the dimension of the resonance hole 6 and the volume of resonance compartment 7. If it were possible to change the thickness of the partition wall 4, the resonance frequency f could of course be varied identically; but it is impractical to do so and the value I is therefore fixed.

FIGS. 1, 2 and 5 are muffler embodiments where the volume of the resonance compartment 7 is variable according to the formula (I), sound entering through opening 2 of the muffler housing 1 and passing through the pipe 11 where highpitched and medium-pitched sound enters through holes 12 into the absorbent means 13 and is muffled. Sound or soundcarrying fluid which is without high and medium pitched sound passes to the sound scattering chamber 9 where the sound waves are scattered to pass through holes 6 into the resonance compartment while carrier fluid leaves through the pipe 8. I

In the compartment 7, the sound due to the resonance phenomenon oscillates at fixed frequency and is reduced. The frequency may be selected at will by changing the volume of compartment 7.

In FIGS. 3-5 the resonance frequency f is set by changing the cross-sectional dimensions of the resonance holes 6 via the handle 25.

The manner in which low-pitched sound is reduced is the same in all embodiments, i.e., as described with reference to FIGS. 1 and 2.

FIGS. 6-11 are embodiments where the device a for muffling low-pitched sound is fixed, that is nonadjustable. FIGS. 6, 7 and 11 especially are muffler embodiments for use with various boilers operated by combusting of gas, liquid or solid fuel.

In FIG. 6 the openings 2,3 and the air pipe 8 are coaxial so smoke is able to pass without any resistance when the device is installed in a chimney or a boiler. Low-pitched sound with smoke is scattered in the sound scattering chamber 9 back of the opening 2 and segregated from the smoke. The scattered sound loses its energy as vibration energy of air and its sound on entering into the resonance compartment 7 via the resonance holes 6.

It is possible to have the device a for low-pitched sound double or in multiples as shown in FIG. 7, with each device muffling low-pitched sound of a different frequency.

In FIG. 6 the velocity V of sound increases because the muffler is to be used with a boiler when the smoke is hot and heats the housing 1.

Now, the velocity V of sound is:

v=33 l .5+0.6lt (m./sec.) wherein t temperature.

Therefore, it is impossible to make a muffler for muffling the low-pitched sound of a boiler without regard to the velocity v ofsound.

FIG. 8 is an embodiment for use in muffling sound at all pitch ranges because of the addition of the device b for mediumand high-pitched sound.

In FIGS. 9-11, sound waves or gas-carrying sound collide with point P and are scattered, to thereafter pass through the two or more branch pipes 28.

The embodiment in FIG. 9 is superior for high-speed fluid having low-pitched sound, because sound and fluid are stopped once by the partition wall and then proceed through the branch pipes 28 to the sound reducing device a for lowpitched sound.

ln FIG. 10 the branch pipe 28 has many absorption holes 12, and middleand high-pitched sound enters into the closed chamber and is effectively reduced by the absorbents 13 of the device b, while low-pitched sound goes through the branch pipe 28 to the sound reducing device a for low-pitched sound where it is reduced by resonance function as mentioned above.

In FIG. ll the sound enters into the resonance compartment 7 through the resonance holes 6 in wall 4 which supports the branch pipes 28, and is effectively reduced in the compartment 7.

lclaim:

l. A muffler comprising, in combination, an elongated tubular housing having a coaxial inlet at one, and an outlet at the other of its ends; a first sound scattering chamber closer to and communicating with said inlet, and a second sound-scattering chamber closer to and communicating with said outlet; a pair of axially parallel passages laterally offset with reference to said inlet and connecting said first sound-scattering chamber with said second sound-scattering chamber; an expansion chamber intermediate said second sound-scattering chamber and sound outlet and communicating via a plurality of apertures only with the former; and at least one circumferentially uninterrupted fluid guidance tube extending in axial direction of said housing through said expansion chamber and connecting said second sound-scattering chamber with said outlet of said housing.

2. A muffler as defined in claim 1; further comprising wall means of circular outline in said housing and separating said expansion chamber from said second sound-scattering chamber, said apertures being provided in said wall means; and a center opening provided in said wall means in communication with said fluid guidance tube.

3. A muffler as defined in claim I, wherein said housing comprises a compartment located between said first and second sound-scattering chambers, said passages extending through said compartment.

4. A muffler as defined in claim 3, wherein said passages are provided with a plurality of holes communicating with said compartment.

5. A muffler as defined in claim 4; and further comprising muffling means surrounding said passages and at least substantially filling said compartment.

6. A muffler as defined in claim 1, wherein said outlet is coaxial with said inlet.

7. A muffler as defined in claim 1, wherein the cross-sectional area of said fluid guidance tube is substantially larger than the cross-sectional are s of the respective apertures. 

1. A muffler comprising, in combination, an elongated tubular housing having a coaxial inlet at one, and an outlet at the other of its ends; a first sound scattering chamber closer to and communicating with said inlet, and a second sound-scattering chamber closer to and communicating with said outlet; a pair of axially parallel passages laterally offset with reference to said inlet and connecting said first sound-scattering chamber with said second sound-scattering chamber; an expansion chamber intermediate said second sound-scattering chamber and sound outlet and communicating via a plurality of apertures only with the former; and at least one circumferentially uninterrupted fluid guidance tube extending in axial direction of said housing through said expansion chamber and connecting said second soundscattering chamber with said outlet of said housing.
 2. A muffler as defined in claim 1; further comprising wall means of circular outline in said housing and separating said expansion chamber from said second sound-scattering chamber, said apertures being prOvided in said wall means; and a center opening provided in said wall means in communication with said fluid guidance tube.
 3. A muffler as defined in claim 1, wherein said housing comprises a compartment located between said first and second sound-scattering chambers, said passages extending through said compartment.
 4. A muffler as defined in claim 3, wherein said passages are provided with a plurality of holes communicating with said compartment.
 5. A muffler as defined in claim 4; and further comprising muffling means surrounding said passages and at least substantially filling said compartment.
 6. A muffler as defined in claim 1, wherein said outlet is coaxial with said inlet.
 7. A muffler as defined in claim 1, wherein the cross-sectional area of said fluid guidance tube is substantially larger than the cross-sectional areas of the respective apertures. 